Molecular cloning of multiple xylanase genes from Pseudomonas fluorescens subsp. cellulosa

Pseudomonas fluorescens subsp. cellulosa was shown to express extracellular xylanases. Genes encoding these enzymes were isolated from a gene library of P. fluorescens subsp. cellulosa DNA, constructed in bacteriophage lambda 47.1. One of the phages (PXC) that expressed xylanase also conferred the ability to hydrolyse carboxymethylcellulose. An 11.8 kb HindIII DNA restriction fragment and a 6.2 kb EcoRI DNA fragment were subcloned from two distinct xylanase-expressing phages, into pUC18, to yield recombinant plasmids pGHJ4 and pGHJ5 respectively. Cells of Escherichia coli harbouring either of these two plasmids, or plasmid pJHH1 (comprising the cellulase gene from PXC, previously cloned on a 7.3 kb partial EcoRI DNA fragment in pUC18), expressed xylanase activity. The positions of the xylanase genes in the recombinant plasmids were elucidated by subcloning and transposon mutagenesis. In pJHH1 the xylanase gene was adjacent to the DNA region encoding the endoglucanase. The polysaccharide-degrading genes in pJHH1 were transcribed from different promotors. Hybridization studies revealed that the xylanase genes encoded by pGHJ4 and pGHJ5 showed strong homology. All three cloned enzymes cleaved p-nitrophenyl beta-D-glucopyranoside and 4-methylumbelliferyl beta-D-cellobioside. Xylan and glucose did not affect expression of xylanase in E. coli strains harbouring pJHH1, pGHJ4 or pGHJ5.